Electrical surge arresters

ABSTRACT

A high voltage (station class) surge arrester comprises a plurality of serially connected stage. Each stage comprises a plurality of low voltage (distribution class) polymer housed solid state surge arresters which are electrically matched. The individual surge arresters of each stage are connected together and to the respective surge arresters of the (or each) adjacent stage by means of cast metal mounting brackets (spiders) having plural equiangularly-spaced limbs to the ends of which the surge arresters are attached. Corona suppression rings are mounted at the top end of the arrester and separate corona suppression components are mounted at the ends of the limbs of the intermediate stages.

FIELD OF THE INVENTION

This invention concerns improvements relating to electric surgearresters, also known as surge diverters, as used in electrical powergeneration and distribution systems for the safe handling ofatmospherically induced surges, arising from lightning strikes forexample, and over-voltages caused by switching operations.

BACKGROUND OF THE INVENTION

We pioneered the introduction of polymer housed solid-state distributionclass surge arresters, as disclosed in GB-A-2188199 for example, and inGB-A-2230661 we proposed the utilization of a series parallelarrangement of a plurality of such distribution class surge arresters asa station class surge arrester. Distribution class surge arrestersgenerally have voltage ratings of the order of 24 to 36 kV and bycoupling together a plurality of electrically matched such distributionclass surge arresters in a series parallel arrangement as described inGB-A-2230661 much higher voltage ratings of the order of 120 to 456 kVcan be accommodated.

Our series parallel station class surge arrester is designed to replacethe conventional porcelain housed station class rester and has beenwidely acclaimed. The present invention concerns improvements in theconstruction of the series parallel arrester.

SUMMARY OF THE INVENTION

Whereas in the series parallel surge arrester described in GB-A-2230661the individual distribution class surge arresters of adjacent serialstages were offset from each other, the present invention proposes toprovide the arrester units in line throughout the series parallelarrangement. Furthermore, whereas in the surge arrester of GB-A-2230661metal mounting plates formed integrally with corona suppression rings attheir peripheries were utilized for interconnecting adjoining stages ofthe series parallel arrangement the present invention proposes a moresimple and cost effective arrangement employing multiple-limbed brakets(spiders) in place of the mounting plates, the distal ends of the limbsbeing provided with corona discharge inhibiting surfaces.

The above and further features of the present invention are set forthwith particularity in the appended claims and will be well understoodfrom consideration of the following description given with reference tothe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE of the accompanying drawing illustrates the upper(top) end of an exemplary series parallel surge arrester according tothe present invention in perspective view.

DETAILED DESCRIPTION OF THE EMBODIMENT

The series parallel surge arrester shown in the accompanying drawingcomprises a plurality of series-connected stages I, II, etc (only thetop two of which are shown) each made up of four electrically matchedsurge arresters 1 which can, for example, be of the kind described inGB-A-2188199 but could be otherwise formed so long as they exhibitsufficient structural integrity. The individual surge arresters 1 ineach stage I, II, etc are coupled together and to the adjoiningarresters of the next adjacent stage by means of cast metal brackets(spiders) 2 having a plurality of limbs 3 extending from a central bodyportion 4 with even angular spacing of 90°. As can be seen, theindividual surge arresters 1 of the different stages are aligned witheach other.

The individual sure arresters 1 have externally screw-threaded endfixing studs S which enable the surge arresters to be affixed to theends of the limbs 3 of the brackets 2, for example by provision of adouble and oppositely screw-threaded locking nut at the end of each limb3 which can be turned with a spanner so as to pull the opposite ends ofthe respective two surge arresters together and into mounting engagementwith the end of the respective limb.

Mounted at the ends of the limbs 3, after attachment of the surgearresters 1, are cast meal corona suppression bodies 6 which can forexample form a push fit onto the ends of the limbs 3 with closeconformance around the ends of the two surge arresters 1 that areattached to the respective limb. The surfaces of the bodies 6 aresmoothly curved as shown to avoid giving rise to excessive fieldvoltages such as might give rise to corona discharge effects.

At the top end of the series parallel arrangement, a corona suppressionarrangement comprising parallel spaced-apart rings 7 and 8 which arecoupled to the limbs 3 of the uppermost mounting bracket 2 by means ofmounting brackets 9.

The illustrated series parallel surge arrester is believed to satisfyelectrical requirements and the mounting brackets 2 and theiraccessories, namely the corona suppression bodies 6 and the resterfixing nuts (not shown), can be manufactured at lower cost than theelectrostatic mounting plates of the series parallel surge arresterdescribed in GB-A-2230661). Furthermore, by virtue of the in lineconnection of the surge arresters of adjacent stages, the overallstiffness of the series parallel sure arrester can be increased ascompared to that of GB-A-2230661. Otherwise the illustrated surgearrester obtains all of the advantages that are described inGB-A-2230661. Modifications and variations are of course possiblewithout departure from the spirit and scope of the intention as setforth in the appended claims; for example, the brackets 2 could havemore or less limbs than the four limbs shown.

1. A high voltage surge arrester comprising a plurality of seriallyconnected arrester stages each of which comprises a plurality ofelectrically matched low voltage surge arresters connected in parallel,the low voltage surge arresters of each stage being connected togetherand to the surge arresters of the or each next adjacent stage by meansof a multiple limbed mounting bracket having corona suppression means atthe end of each limb.
 2. A high voltage surge arrester as claimed inclaim 1 wherein at the top of the surge arrester the corona suppressionmeans comprises at least one corona suppression ring.
 3. A high voltagesurge arrester as claimed in claim 1 wherein the corona suppressionmeans at the ends of the limbs of the mounting bracket supporting theends of adjacent serial stages of the arrester comprise individualbodies associated each with a respective one of the limbs.
 4. A highvoltage surge arrester as claimed in claim 1 which is adapted forstation class operation and wherein the low voltage surge arresters aredistribution class surge arresters.
 5. A high voltage surge arrester asclaimed in claim 1 wherein the low voltage surge arresters are polymerhoused solid state surge arresters.
 6. A high voltage surge arrestercomprising: a plurality of serially connected arrester stages, each ofsaid stages including a plurality of electrically matched low voltagesurge arresters connected in parallel; a multiple limbed mountingbracket connecting each of said stages together so that arresters ofeach stage are aligned along a common line with arresters of an adjacentstage; and corona suppression means supported on said multiple limbedmounting bracket.
 7. A high voltage surge arrester comprising: firstplurality of electrically matched low voltage arresters spaced apart andparallel to each other; a second plurality of electrically matched lowvoltage arresters in line with said first plurality of arresters; and afirst bracket having radial limbs which connect first ends of said lowvoltage surge arresters of said first plurality of arresters to firstends of said surge arresters of said second plurality of arresters,forming a series circuit between parallel connected first and secondplurality of surge arresters.
 8. A high voltage surge arrester accordingto claim 7 further comprising: a first corona suppression meanssupported to said radial limbs.
 9. The high voltage surge arresteraccording to claim 8 comprising: a second bracket connected to aremaining end of said first plurality of electrically matched lowvoltage arresters; and said second bracket supporting a second coronasuppression means.
 10. The high voltage surge arrester according toclaim 9 wherein said second corona suppression means comprise a pair ofparallel spaced apart ring.